For the caramel sauce: Place the sugar, golden syrup and water in a heavy-bottomed pan and stir to combine. Heat over a medium-high heat, occasionally swirling the pan, until it turns a medium gold amber colour - this will take about 10 minutes. Then remove the pan from the heat and carefully whisk in the cream, the mixture will bubble up so be careful. Then stir in the butter and vanilla extract, until combined. Pour into a heat-safe container (a pyrex bowl, jug or a jam jar will do) and set aside to cool and thicken.
For the base: Line the base of an 9in spring form tin with baking paper and set aside. Then blitz the digestives in a food processor until they are fine crumbs. Pour in the melted butter and blitz again until it starts to hold together. Tip this into your lined tin, and using a spoon (or your hands), compact the base down. Then place in the fridge to chill for 20 minutes.
For the cheesecake filling: Using an electric hand-whisk beat the cream cheese and icing sugar together in a large bowl. Then whisk in the double cream until the mixture thickens. Finally, stir in 150g of the cooled and thickened caramel until fully combined. Pour the cheesecake mixture on top of the chilled base and level. Then cover with clingfilm and leave in the fridge overnight or for at least 4 hours to completely set. Cover the remaining caramel, and also keep in the fridge.
To decorate: When you are ready to serve, decorate your cheesecake with the remaining caramel however you like. To create the feathered effect like I did, place the caramel into a piping bag and snip off the end to create a small hole. Then pipe vertical lines across the whole cheesecake. Take a chopstick/skewer or cocktail stick and drag through the lines horizontally in alternate directions to create a feathered effect.